The goals of this protocol are (1) to determine the safety, minimum effective dose, maximum tolerated dose, and preliminary efficacy of d4T administered to infants and children 12 years of age and under; and (2) to establish pharmacokinetic parameters of d4T in children 12 years of age and under. ("D" protocol). The study has closed to subject follow- up. Primary study results were published in PEDIATRICS. This study established a basis for two Pediatric ACTG studies(ACTG 240 and ACTG 327).